I think the small ones are out of stock at the moment for about 2 months...
The other one is going for about 96 Euros. Ebay might be your best bet.
Although the PCB is available.... You could always have ago at building it yourself?!

If you're going to put something on.... Don't brag, Just do; and for God's sake - do it properly!!!

Whatever you buy I strongly advise you to buy one that locks to your pilot. Some are just free-running 57khz oscillators - although they may display station name in ideal situation they don't play nicely with all radios.

It is best practice to regenerate / lock 57kHz to pilot tone of stereo coder. That way, both will be in phase and will cause less (or none) choped audio. Also, i don't feel good about this 100€ DSP solutions. Good and well filtered DSP will cost more than that. And for that money, you can build very nice analog encoder.